Understanding the Kelvin-Planck Statement

The question asks to identify the correct Kelvin-Planck statement related to thermodynamics. This statement is a crucial part of the Second Law of Thermodynamics, which governs the direction of heat flow and the efficiency of converting heat into work.

The Kelvin-Planck Statement

The Kelvin-Planck statement specifically addresses the limitations of heat engines. It states that:

• It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work.

This means that a heat engine must interact with at least two thermal reservoirs: a high-temperature source from which it receives heat, and a low-temperature sink to which it rejects some heat. It cannot convert all the absorbed heat into useful work.

Analyzing the Options

Let's evaluate each option provided:

Option 1: Clausius Statement

This option states: "It is impossible to construct a device which operates in a cycle and produces no effect other than the transfer of heat from a cooler body to a hotter body".

This describes the Clausius statement, which relates to the operation of refrigerators and heat pumps. It requires external work to move heat from a cold reservoir to a hot reservoir. Therefore, this is not the Kelvin-Planck statement.

Option 2: Kelvin-Planck Statement

This option states: "It is impossible for a heat engine to produce net work in a complete cycle if it exchanges heat only with bodies at a single fixed temperature".

This is the accurate definition of the Kelvin-Planck statement. It correctly highlights the impossibility of a perpetual motion machine of the second kind – a machine that could continuously convert heat entirely into work from a single heat source.

Option 3: Heat Can Be Converted Into Work

This statement, "Heat can be converted into work," is fundamentally true and is the basis for how heat engines operate. However, it does not capture the limitations specified by the Kelvin-Planck statement. The First Law of Thermodynamics allows this conversion, but the Second Law imposes restrictions on the efficiency and process.

Option 4: Work Can Be Converted Into Heat

The statement "Work can be converted into heat" is also true. Examples include frictional heating or electrical resistance. This process does not violate the Second Law of Thermodynamics. However, it is unrelated to the specific principle articulated by the Kelvin-Planck statement concerning heat engines.

Option 5:

This option is empty and provides no statement to evaluate.

Conclusion on the Kelvin-Planck Statement

The Kelvin-Planck statement is a fundamental principle of the Second Law of Thermodynamics, defining the necessary conditions for a heat engine to operate and produce work. Option 2 correctly represents this principle.